TheHitchhikers GuideTo The Galaxy

Earth Edition

Conservation Genetics

Conservation genetics is part of the broader field of conservation biology. Conservation biologists study species affected by problems such as habitat loss through environmental changes and exploitation. The information studied can be used to make informed decisions for the future, as well as help conserve diversity in the present.

Genetics can give insight into the diversity of a population and add to the understanding of ecosystem managers (the people who make the decisions about how to conserve ecosystems). Despite its seemingly exact name of 'Conservation Genetics', this field is made up of all kinds of individual sciences; ecology, mathematics, molecular biology, the study of family trees (evolutionary systematics) to name but a few.

Genetic conservationists have one question in mind throughout their work: 'Why is this species so near to extinction, and how can we bring it back with the diversity needed to ensure the continuation of the species?'

Preservation vs Conservation

An important concept for conservation genetics is the difference between the preservation of a species and the conservation of a species. Preservation implies only keeping the species alive (ensuring enough breeding individuals to continue their unique genome). The idea behind conservation, however, keeps as many individuals alive as possible and tries to ensure genetic diversity among them.

Conservation should maximise the number of individuals in the population, because that usually equals the most diversity in that population. We can see this through observation and the principles of genetics. Observation shows us that the more individuals in a population, the more diverse its members are - humanity serves as a good example of this. It also makes sense from a genetic and evolutionary standpoint: the more individuals, the more likely that useful mutations or unique crossing-over will occur, creating genetically diverse beings.

Genetic Diversity

Genetic diversity is defined as the number of versions (alleles) of a gene that a specific species contains. When most organisms in a population have only one version (allele) for a gene, then the diversity of that gene among that population is low.

When there is low genetic diversity among a population, then it becomes more likely that the species will be wiped out through random events. Alleles are the different forms of a single gene: eye colour is an easy-to-understand example, although excessive simplification is never quite correct - the allele for blue eyes and the allele for brown eyes are both found in relatively the same position on the chromosome and they are both different representations of the same gene. However, although they are examples of the same gene, they code for different results.

Conservation genetics seeks to realise the extent of diversity in a population and keep it as high as possible to lessen the likelihood of the loss of the entire species.

Loss of Diversity

There are a number of ways in which loss of genetic diversity can occur. Most of them are known to the general population, but the general population doesn't necessarily always think in terms of conservation genetics.

Population Bottleneck - Population bottlenecks occur when the number of individuals in the population suddenly drops to tiny numbers. The few individuals that survive are known as 'founders' and only their genes can be passed on to future generations. Any genetic disorder affecting an organism in the newly founded population will affect a proportionately high percentage of all the offspring of that species, casting a shadow over the long term success of the remaining population. Most of our endangered species have had a population bottleneck in their past.

Random Genetic Drift - In random genetic drift, the frequency of allele occurrence in a population changes over time. This is most severe for small populations, in which a little change can have a lot of impact. The genetic variability lost after each generation can be estimated by the formula 1/(2Ne), where Ne is the effective population size (the effective population size being basically the number of breeding individuals in the population). A population of 100 individuals would therefore lose 0.5% of their total genetic variability each generation, while a population of 10 individuals would lose 5% after each generation. After just a few generations, more than half the original variability in a small population could be lost forever. Low variability, of course, results in less ability to adapt to new changes and a higher likelihood of extinction.

Inbreeding -Inbreeding can cause many otherwise unrepresented alleles to show up in the population. Many dangerous alleles are recessive and hidden when the carrier is heterozygous1. The more closely related two individuals are, the more likely that they will have the same genotype2; therefore it becomes much more likely that their children will have the harmful recessive trait. In a large population, the probability of finding an unrelated mate is much higher than it is in a small population.

Implementation of Conservation Genetics

We use conservation genetics when we know that there might be a problem affecting a species' survival soon (like the destruction of a habitat), or when the population of a species dwindles too much for our continued comfort.

After deciding that there may be a problem in a species' future, management techniques go into affect. Scientists do the following things, usually in this order:

Decide which species will be studied. (There are so many species in our world that endangered and threatened ones usually get priority).

Look at the form of a species. What are its immediate and known relatives?

Examine the genetic diversity in various populations of the species and the flow of genes between these populations. These data are analysed using mathematical models.

Because Conservation Genetics extends back to the habitat, conservationists spend time observing the habitat as well. They:

Look at the species' degree of adaptability to different habitat conditions (for instance, pH differences for plants).

Examine other species in the habitat that are important to the study species (food sources, pollinators, and predators, to name a few).

Address threats to the habitat's stability. (Human and climate threats are the largest categories).

Uses of Genetics in Conservation

Genetics can help us determine how closely related certain species are, through protein comparison, the comparison of chromosome number, or comparative genomics3. Chromosome number differs rather often in plants, through polyploidy (that is, having extra copies of the chromosome set), or chromosome deletion. Protein comparison can also be used in the identification of related species, because proteins are coded for by DNA (therefore different DNA can result in different proteins).

It is relatively easy to lose species without the aid of conservation genetics, as can be shown by a short cause-effect paragraph:

A species loses its habitat due to human intervention (we want to build some condominiums on top of a gopher home, not recognising that this particular species of gopher does not exist anywhere else in the world). The population size of these gophers dwindles to perhaps 15 individuals through loss of habitat. The low population size also results in different gender-to-gender ratios among these gophers. Now the effective population size approaches zero. Inbreeding occurs, in an attempt to save the population. The allele frequency and alleles contained in that population go askew, and the gophers become extremely susceptible to disease. An epidemic is enough to finish them off.

Without Conservation Genetics, we could be trying to conserve one population of 1000 individuals and relatively large genetic diversity (remember that conservation is very expensive), while another population of 1500 individuals is much closer to extinction due to their nearly non-existent diversity. It is genetics that lets us know this, and it is genetics that can give us answers to all our other questions necessary to the successful conservation of as many species as possible.

1Heterozygosity is the state of having both a dominant and recessive allele (version) of a trait. The dominant trait is most usually the one that will be shown in the organism's physical appearance. Also, it is generally recognised among genetic conservationists that heterozygous organisms are the ones most 'fit' in the Darwinian sense: they have the best of both worlds, so to speak, and if needed can draw on either allele for survival. Individuals with two copies of the same allele are known as homozygous, and are considered less 'fit' because they only have one allele option.2An organism's genotype is its genetic make-up, which gene forms it has. (The gene forms are more scientifically known as alleles.) An organism's phenotype is composed of the physical traits resulting from this genetic makeup.3Comparative genomics stays in the same broad field as 'comparison of chromosome number', but includes the comparing of all of the individual genes of one species to other species. This is a relatively new field, because we have only recently found species gene-maps.

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